Method for preparing a space between adjacent vertebrae to receive an insert

ABSTRACT

A device and method for use in a human spine to prepare a space between adjacent vertebral bodies and into the vertebral end plates to receive an implantable insert. The device includes a handle, a shaft, and a mounting member at one end of the shaft. An abrading element is mounted on the mounting member and is coupled to a drive mechanism. The drive mechanism is operable to move the abrading element in at least one degree of freedom to create surfaces having predetermined contours in the end plates of the adjacent vertebral bodies.

This is a continuation, division of application Ser. No. 09/608,955,filed Jun. 30, 2000 now U.S. Pat. No. 6,537,279, which is a continuationof 09/094,036, filed Jun. 9, 1998, now U.S. Pat. No. 6,083,228, issuedJul. 4, 2000—all of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a device for insertion into a discspace between adjacent vertebral bodies in the human spine, and a methodof working on those portions of the vertebral bodies adjacent that discspace to remove bone material and thereby access vascular bone. Thedevice and associated method forms a surface on each of the vertebralbody surfaces that are adjacent the intervertebral disc space, eithersequentially, or in an alternative embodiment, simultaneously. Theformed surface(s) have a shape and a contour corresponding to aninterbody spinal insert to be implanted in the disc space.

BACKGROUND OF THE INVENTION

Inserts for placement between adjacent vertebrae in the spine come in avariety of shapes and sizes and are made of a variety of materials. Suchinserts may or may not be designed to promote fusion of the adjacentvertebral bodies. Inserts not intended to participate in or to promotefusion of the adjacent vertebrae, for example an artificial spinal disc,are intended to maintain the spacing between the adjacent vertebrae andto permit relative motion between those vertebrae. Such inserts may ormay not include some type of surface treatment or structure designed tocause the vertebrae to attach and grow onto the surface of the insert tothereby stabilize the insert. Another type of insert comprises bonegrafts. Such bone grafts are typically intended to participate in and topromote fusion of the adjacent vertebrae. Another type of insert for usein human spinal surgery comprises implants made of selected inertmaterials, such as titanium, that have a structure designed to promotefusion of the adjacent vertebrae by allowing bone to grow through theinsert to thereby fuse the adjacent vertebrae. This last type of insertis intended to remain indefinitely within the patient's spine.

The first known example of this last type of insert (for use in humans)is described in U.S. Pat. No. 5,015,247, which, in its preferredembodiment, discloses a hollow, threaded, cylindrical, perforated fusionimplant device made of a material other than and stronger than bone andwhich is intended to cause fusion of adjacent vertebral bodies. A fusionpromoting material, such as cancellous bone for example, is packedwithin the hollow portion of the implant and participates in the fusion.As used herein, the term fusion defines the growth of bone tissue fromone vertebral body across a disc space to an adjacent vertebral body tothereby substantially eliminate relative motion between those vertebrae.

Human vertebral bodies are comprised of a hard outer shell of corticalbone (sometimes referred to as the cortex) and a relatively softer,inner mass of cancellous bone. Just below the cortical bone is a layerreferred to as the subchondral plate. The outer shell of cortical bonethat is adjacent the disc and the underlying subchondral plate aretogether herein referred to as the “end plate” and, for the purposes ofthis application, is hereby so defined to avoid ambiguity. The spinaldisc that resides between adjacent vertebral bodies maintains thespacing between those vertebral bodies and, in a healthy spine, allowsfor relative motion between the vertebrae. At the time of surgery, forexample in the instance where fusion is intended to occur betweenadjacent vertebral bodies of a patient's spine, the surgeon typicallyprepares an opening at the site of the intended fusion by removing someor all of the disc material that exists between the adjacent vertebralbodies to be fused. Because the outermost layers of bone of thevertebral end plate are relatively inert to new bone growth, the surgeonmust work on the end plate to remove at least the outermost cell layersof bone to gain access to the blood-rich, vascular bone tissue withinthe vertebral body. In this manner, the vertebrae are prepared in a waythat encourages new bone to grow onto or through an insert that isplaced between the vertebrae.

Present methods of forming this space between adjacent vertebraegenerally include the use of one or more of the following: hand heldbiting and grasping instruments known as rongeurs; drills and drillguides; rotating burrs driven by a motor; and osteotomes and chisels.Sometimes the vertebral end plate must be sacrificed as occurs when adrill is used to drill across the disc space and deeper into thevertebrae than the thickness of the end plate. Such a surgical procedurenecessarily results in the loss of the hardest and strongest bone tissueof the vertebrae—the end plate—and thereby robs the vertebrae of thatportion of its structure best suited to absorbing and supporting theloads placed on the spine by everyday activity. Nevertheless, thesurgeon must use one of the above instruments to work upon the adjacentend plates of the adjacent vertebrae to access the vascular, cancellousbone that is capable of participating in the fusion and causing activebone growth, and also to attempt to obtain an appropriately shapedsurface in the vertebral bodies to receive the insert. Because the endplates of the adjacent vertebrae are not flat, but rather have acompound curved shape, and because the inserts, whether made of donorbone or a suitable implant material, tend to have a geometric ratherthan a biologic shape, it is necessary to conform the vertebrae to theshape of the insert to be received therebetween.

It is important in forming the space between the adjacent bonestructures to provide a surface contour that closely matches the contourof the inserts so as to provide an adequate support surface across whichthe load transfer between the adjacent bone structures can be evenlyapplied. In instances where the surgeon has not been able to form theappropriately shaped space for receiving the inserts, those inserts mayslip or be forcefully ejected from the space between the adjacentvertebrae, or lacking broad contact between the insert and thevertebrae, a failure to obtain fusion may occur.

Furthermore, no known prior art device for preparing the vertebral endplates to receive an insert includes a working element that correspondsin shape, size, or contour to the shape of the insert to be implanted.That is, the known devices must be moved from side to side and in andout within the intervertebral space by an amount that exceeds thedimensions of the working element of the device, e.g., the rotating burrof a motor driven routing instrument or the working end of knownosteotomes and chisels.

OBJECTS OF THE PRESENT INVENTION

It is an object of the present invention to provide a device and methodfor quickly, safely, effectively, and accurately working upon avertebral body end plate adjacent a disc space so as to, whilepreserving that end plate at least in part, remove bone to produce areceiving surface corresponding in size, shape, and contour to an insertto be implanted between the adjacent vertebrae.

It is a further object of the present invention, in at least certainembodiments, to provide a device capable of simultaneously working uponboth of the vertebral body end plates adjacent a disc space to produceopposed receiving surfaces in the adjacent end plates corresponding insize, shape and contour to an insert to be implanted, and in so doing todefine the shape to the insert space.

It is a further object of the present invention to provide a vertebralinterspace preparation device that, in a preferred embodiment, iscapable of working with linear insertion, i.e., insertion along a singleaxis, and without the need to substantially move the device from side toside within the disc space along a second axis. In such a preferredembodiment, the device has at its working end an abrading element havinga width generally corresponding to the width of the insert to beimplanted.

It is a further object of the present invention to have a safetymechanism built into the device that limits the depth of insertion ofthe device into the spine.

It is a further object of the present invention to provide a vertebralinterspace preparation device that has interchangeable ends so as to becapable of producing a variety of differently sized and contouredsurfaces and shapes within the intervertebral space.

It is a further object of the present invention to have abradingsurfaces extending to the leading end of the device such that the devicemay remove bone along its leading end as it is advanced within the discspace.

These and other objectives of the present invention will occur to thoseof ordinary skill in the art based on the description of the preferredembodiments of the present invention described below. However, not allembodiments of the inventive features of the present invention needachieve all the objectives identified above, and the invention in itsbroadest aspects is not limited to the preferred embodiments describedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial top view of a first preferred embodiment of a deviceembodying the present invention, which device includes an abradingelement having a single abrading surface;

FIG. 1A is a full top view of the device of FIG. 1 illustrating thehandle of the device;

FIG. 2 is a side view of the device shown in FIG. 1;

FIG. 3 is an end view of the device shown in FIGS. 1 and 2;

FIG. 4 is a second top view of the device shown in FIG. 1 and alsoillustrates the preferred range and type of motion of the abradingelement;

FIG. 4A is a partial view of the device of FIGS. 1-4 showing a preferredmechanism for connecting the handle to the device shaft;

FIG. 5 is a detailed view of a portion of the device shaft illustratingnotches used to hold a stop member in a selected position;

FIG. 6 is a detailed view of a spring-biased lever mechanism that may beused to adjust the position of a stop member;

FIG. 7 is a detailed view of a coupling mechanism that may be used tomovably couple the drive mechanism to the abrading element;

FIG. 8 is a detailed view of the mounting member disposed at the distalend of the device shaft;

FIG. 9 is a further detailed view of the coupling mechanism and mountingmember illustrated in FIGS. 7 and 8;

FIG. 10 is a detailed view illustrating a preferred way of movablyconnecting the coupling mechanism to the abrading element;

FIG. 11 is top view of a first vertebral body having a surface preparedin one of the end plates by a device incorporating the presentinvention;

FIG. 12 is a top view of a second vertebral body, different than thatshown in FIG. 11, having a surface prepared in one of the end plates bya device incorporating the present invention;

FIG. 13 is a cutaway side view of the vertebral body shown in FIG. 12;

FIG. 14 is a cutaway side view of adjacent vertebral bodies having theirrespective adjacent end plates prepared by a device incorporating thepresent invention to form a space configured to receive an insert;

FIG. 15 is an exaggerated perspective view of the vertebral bodyillustrated in FIG. 12 showing the formation of the receiving surface inthe vertebral end plate;

FIG. 15A is a top view of a section of a human spine illustrating theportion of the disc that is typically removed to accommodate theimplantation of an intervertebral insert;

FIG. 16 is a top view of a second preferred embodiment of a deviceembodying the present invention, which device includes an abradingelement having two abrading surfaces;

FIG. 16A is a top view of the device of FIG. 16 illustrating irrigationand suction tubes that may be incorporated into the device;

FIG. 17 is a side view of the device shown in FIG. 16;

FIG. 17A is a side view of the device shown in FIG. 17;

FIG. 17B is a detailed view of one possible drive mechanism that may beused with the second embodiment of the present invention;

FIG. 18 is an alternative embodiment of an abrading element having twoabrading surfaces, which abrading surfaces are inclined relative to oneanother to form a space between the adjacent vertebral bodies thatapproximates the lordotic curvature of a human spine at the locationthat will receive the interbody insert;

FIG. 19 is a cutaway side view of adjacent vertebral bodies showing alordotically configured space created between the vertebrae by theabrading element shown in FIG. 18;

FIG. 20 shows an alternative embodiment of a mechanism for driving anabrading element;

FIG. 21 illustrates an alternative path of motion possible for anabrading element according to the present invention;

FIG. 22 illustrates a further alternative path of motion possible forthe abrading element; and

FIG. 23 illustrates an alternative configuration of the abrading elementsuitable for creating concave insert receiving surfaces on the adjacentvertebral end plates.

SUMMARY OF THE INVENTION

The device, in its preferred embodiment, generally comprises an abradingelement movably and replaceably mounted on the distal end of a shaft,and a depth limiting mechanism to control the depth of insertion of theabrading element into the intervertebral space (i.e., the disc space).The device also includes a handle that may be detachable from the shaft.As used herein, the term “handle” refers to a portion of the device thata surgeon may grip or otherwise manipulate to guide the working end ofthe device. That “handle” may, in fact, have multiple purposes. Forexample, the handle may be a portion of the shaft on which the abradingelement is mounted at one end. Alternatively, the handle may be part ofa segment that connects the device to a power source, for example, partof a conduit that supplies pressurized gas if the power source isturbine driven. In any event, the term “handle” is used herein in itsbroadest context to refer to that portion of the device that the surgeonchooses to grasp.

Additionally the shaft may be detachable from the abrading element. Thedevice also includes a drive mechanism for transmitting power toactivate, i.e., move, the abrading element, and the drive mechanism isconnected to an energy source, e.g., a rechargeable battery, that may behoused within the handle of the device. By way of example only, thedrive mechanism may comprise an electric motor or an electromagneticoscillating mechanism. Or, again by way of example only, the drivemechanism and handle in which it is disposed may comprise the head unitof a gas powered turbine of the type commonly used in other surgicalinstruments.

In the preferred embodiment, the abrading element is generally as wideas the insert to be implanted between the adjacent vertebral bodiesadjacent the disc space. The receiving bed, i.e., the prepared surfaceof the vertebrae, when formed by the device, will correspond in shape,size, and contour to the corresponding surfaces of the insert to beimplanted. By way of example only, the surface produced may be flat orconcave, or of some other desired shape and size so as to correspond tothe upper or lower vertebrae contacting surfaces of the insert that willbe implanted between the vertebrae. The device may also include aleading end that is capable of cutting through bone and/or disc materialto form a pocket having a contour corresponding to the forward aspectand leading end of the insert to be implanted.

In a first preferred embodiment, the abrading element includes a singleabrading surface that works on one vertebral surface at a time withinthe disc space.

In a second preferred embodiment, the abrading element includes a pairof opposed, outwardly facing abrading surfaces which lie in planes thatmay be either parallel to each other or, alternatively, convergent toeach other. This embodiment of the present invention offers the furtherbenefits of saving time by simultaneously preparing both of thevertebral end plates adjacent a disc space. The second embodiment notonly includes the ability to simultaneously create two opposed surfaces,but also to shape the three-dimensional space that will be createdbetween the adjacent vertebrae, which shape can be made to conform tothe desired lordosis of that portion of the spine that will receive theinsert.

However, the abrading element of the present invention is not limited tobeing a unitary, one piece construction, regardless of the number ofabrading surfaces the abrading element may have. The abrading elementmay comprise multiple pieces that, by way of example and not limitation,are mountable on the end of the device to, in combination, define theoverall shape of the abrading element and its abrading surface orsurfaces. Thus, the term “abrading element” is used herein to refer toboth a unitary, one piece construction or a multi-piece construction.

Thus, the present invention provides a device and method for preparing adisc space between adjacent vertebral bodies to receive an insert, andprepares that disc space by removing a portion of the end plate of thevertebrae adjacent that disc space to form predetermined surfaces in theend plates. The prepared surfaces are sized and contoured to have broadintimate contact with the insert to be implanted between the adjacentvertebrae, which broad contact provides for increased implant stability.This broad area of intimate contact between the vertebrae and the insertpromotes bone ingrowth from the vertebrae into the insert, and alsoprovides a broad area over which to support the incumbent loads so as tominimize the risk of vertebral collapse or subsidence of the insert intothe vertebra.

The abrading element is mounted on the mounting member and may beremovable and interchangeable. In such an embodiment, the mountingmember may be, but does not have to be, attachable to a shaft that isattachable to the handle. The abrading element and the mounting membermay be separable from each other. Alternatively, the abrading elementand the mounting member may, together, be removable from the handle.Various configurations of the abrading element and its abrading surfaceor surfaces can be used to form various contours in the adjacentvertebral bone structures.

In the instance where the abrading element has one abrading surface, theopposite surface of the abrading element, or the opposite surface of themounting member, may be specifically designed to be non-abrading to theopposed adjacent vertebral end plate. Such a non-abrading surface may bedesigned to provide a mechanical advantage (such as achieved with afulcrum) to allow the surgeon to increase the pressure of the abradingsurface against the end plate being worked on, and, further, may becurved so as to be centering within the disc space by contact with avertebral surface.

While the preferred embodiment of the present invention is discussed anddisclosed herein with respect to creating a space between adjacentvertebrae in the spine, the present invention is not limited to a devicefor creating a space between adjacent vertebrae, but can also be used inother portions of the body where it is desirable to place an insertbetween adjacent bone structures. Furthermore, and as alluded to above,an embodiment of the present invention may have upper and lower abradingsurfaces that are in angular relationship to each other so as to, forexample, match the natural lordotic curvature of the human spine at thelocation of the vertebrae to be operated upon. Similarly, certain of theabrading surfaces of the abrading element may be configured with aconvex, or even compound, geometry so as to form surfaces in theadjacent bone structures having a desired contour. Additionally,sequentially larger ones of the abrading element, or mounting member,may be used to form the desired space in a step-wise fashion, or theabrading element may be sized to substantially match the final desiredwidth of the surface to be formed in the vertebral end plate.Furthermore and also as noted above, the abrading element may beconfigured with a sharpened leading edge to allow the abrading elementto “forward cut” as it is inserted between the adjacent vertebrae. Inthis manner, progressive insertion of the abrading element between thevertebrae can be facilitated.

While the present invention has been generally described above, and thepreferred embodiments of that invention will be described in detailbelow, neither that general description nor the detailed descriptionlimits the scope of the present invention. That scope is defined solelyby the claims appearing at the end of this patent specification.

DETAILED DESCRIPTION OF THE PRESENTLY CONTEMPLATED EMBODIMENTS

With reference to FIGS. 1 and 1A, a first embodiment of the presentinvention comprises a disc space preparation device generally referredto by numeral 10. Device 10 includes a shaft 12 and a handle 13. Handle13 may be formed with any number of known shapes designed to make thesurgeon's grip on the handle more secure or comfortable. Similarly,handle 13 may include a soft rubber covering or may be formed, at leastpartially, of a material designed to promote a secure grip of thesurgeon's hand on the handle. Those of ordinary skill in the art willrecognize the many types of surface configurations or materials of whichthe handle can be made to achieve these goals.

With continued reference to FIGS. 1 and 1A, disposed within handle 13 isa drive mechanism diagrammatically depicted by box 14. Although in theembodiment of the device shown in FIGS. 1 and 1A the drive mechanism 14is disposed within handle 13, it need not be disposed in the handle. Thedrive mechanism may be disposed completely or partially outside of thehandle, for example, where the drive mechanism is a gas powered turbineelement such as is used in some known surgical instruments. Drivemechanism 14 is operably connected to the proximal end of shaft 12 andis capable of moving an abrading element 18 disposed at a distal end 15of shaft 12. Abrading element 18 has an abrading surface 19. Drivemechanism 14 moves abrading element 18 at a sufficiently high rate toquickly and efficiently cause abrading surface 19 to form the desiredspace and the desired surface contours in the adjacent vertebral bonestructures. As illustrated in FIG. 2, the abrading element 18 is mountedon a mounting member 16 disposed at the distal end 15 of shaft 12. Inthis embodiment, the mounting member is fixed to shaft 12 and only theabrading element moves. However, many alternative mechanisms formounting the abrading element on the device are possible within thescope of the present invention, including a mechanism wherein mountingmember 16 is movably attached to shaft 12 and the drive mechanism movesboth the mounting member and the abrading element attached thereto.Also, mounting member 16 may be designed with a surface 17 on the sideof the mounting member 16 opposite abrading element 18. Surface 17 isdesigned, in the embodiment shown, to bear against the end plate that isopposite the end plate being worked on by abrading element 18. In thismanner, surface 17 provides a bearing surface that the surgeon may useto gain a mechanical advantage (such as with a lever) to contactabrading surface 19 of abrading element 18 against the end plate beingworked on. Additionally, surface 17 may be curved as shown in FIG. 2, orotherwise shaped, to contact one end plate and, thereby, center orotherwise position abrading element 18 in the disc space.

As presently contemplated, the motion of the abrading element may bevibratory, reciprocatory, oscillatory, or rotary. In the first preferredembodiment of device 10, the motion of the abrading element is rotary ina clockwise then counterclockwise direction through a preferred range ofmotion of between 20° to 45°, as illustrated in FIG. 4. Whatever typeand range of motion is selected for the abrading element, it willlikely, although not necessarily, be in a direction that is generallyparallel to the plane of the surface to be formed in the vertebral endplate. However, since the shape of that surface contour is notnecessarily flat, neither is the direction of the motion of the abradingelement necessarily parallel to all points on that desired surfacecontour.

By way of example and not limitation, the drive mechanism may comprise amagnetic driver of the type described in U.S. Pat. No. 5,263,218.Alternatively, the drive mechanism may take the form of a mechanicaldrive utilizing a cam mechanism such as described in U.S. Pat. No.5,383,242. Additionally, drive mechanisms used in known surgical powermilling apparatus may also be used. As presently contemplated, the drivemechanism should be capable of moving the abrading element and itsabrading surface or surfaces at a speed sufficient to abrade the hardcortical bone of the vertebral end plate. The working range and speed ofmotion of the drive mechanism will be readily selected by those of skillin the art.

In one embodiment of the present invention utilizing reciprocatingmotion, the stroke or amount of reciprocating movement is relativelysmall and can be selected as desired to achieve the purpose of abradingthe adjacent bone structures. That stroke may be selected based on therelative strength of the bone structures to be abraded, the relativestrength of the material forming the abrading element, and the type ofsurface roughening formed on one or more surfaces of the abradingelement. This relatively small reciprocating movement of the abradingelement results in a tightly controlled excursion area between theadjacent vertebrae being prepared to receive an insert. In contrast, amotorized burr must be moved free hand and in a side-to-side motionwithin the disc space by the surgeon to form a space to receive aninsert. Thus, use of such a motorized burr does not provide a way offorming a precise surface shape in the vertebral end plate.Additionally, because the motorized burr rotates in a single direction,it may catch on a piece of the vertebra and cause the burr to jerkforcefully out of the intervertebral space. Such an occurrence will nothappen with the device 10 because of the controlled excursion of thedevice.

In the first embodiment of the present invention described herein, drivemechanism 14 is powered by a rechargeable battery illustrated as box 66in FIG. 1A. Battery 66 is also preferably located within handle 13 ofdevice 10. However, the present invention is not limited to use with arechargeable and/or replaceable battery 66, but may also be configuredto run on any standard electrical source, such as 110 volt, 60 cyclepower sources, with or without the accompanying use of a transformer toreduce that voltage as may be necessary and desirable. Alternatively,the drive mechanism may comprise a gas turbine mechanism as is commonfor many types of powered surgical instruments. The particular powersource that powers drive mechanism 14 does not form a part of thepresent invention except to the extent it is adapted to achieve theappropriate and desirable amount of movement of the abrading element.

Referring now to FIG. 2, which shows a portion of device 10 in sideview, mounting member 16 extends from the distal end 15 of shaft 12. Asdescribed below with reference to FIGS. 7–10, the mounting member may beconfigured to house a portion of a coupling mechanism that, in turn,couples drive mechanism 14 to an abrading element 18 to move theabrading element in at least one degree of freedom while the mountingmember remains stationary relative to the handle. The term “degree offreedom” is used herein in its ordinary sense to refer to motion in astandard three-dimensional environment. That three dimensionalenvironment may be defined by X, Y, and Z axes. In such athree-dimensional environment, 6 degrees of freedom exist: translationalmotion along each of the X, Y, and Z axes, and rotational motion abouteach of the X, Y, and Z axes. Thus, drive mechanism 14 is operable tomove abrading element 18 in a reciprocating, oscillating, or vibratingmotion transversely along one or more of the X, Y, and Z axes.Alternatively, or in conjunction, drive mechanism 14 may be configuredto move abrading element 18 around one or more of the X, Y, or Z axes.Of course, for purposes of achieving the objectives of the presentinvention, it may not be necessary that the drive mechanism reciprocateor oscillate mounting member 16 in anything more than a single degree offreedom.

Referring now to FIGS. 7–10, in a present preferred embodiment, abradingelement 18 includes a projection 20 (as best seen in FIG. 10) that is tobe received in a corresponding aperture 21 formed in mounting member 16(as best seen in FIG. 8). Mounting member 16 may be fixedly disposed ondistal end 15 of shaft 12. Alternatively, mounting member 16 may beremovably attached to distal end 15 of shaft 12. In the presentembodiment, a coupling mechanism is used to couple abrading element 18to mounting member 16 and to the drive mechanism. FIG. 10 illustratesthat coupling mechanism with mounting member 16 removed to show inclearer detail the coupling mechanism.

With reference to FIGS. 7 and 9, the coupling mechanism in the firstpreferred embodiment of the present invention comprises a generallytubular member 100 received within a hollow, longitudinal aperture ofshaft 12. Tubular member 100 includes a proximal end 102 and a distalend 104. A T-shaped connector 108 is configured at the end of a driverod 112. Drive rod 112 is adapted to be received within a correspondingaperture 110 in tubular member 100. A pivot rod 114 extends from thedistal end 104 of tubular member 100 and is adapted to fit in acorresponding hole 115 formed in mounting member 16 at the end of shaft12.

With reference to FIG. 8, mounting member 16 includes a central aperture21 and an oblong slot 23 formed through a wall of mounting member 16.Slot 23 is configured to allow connector 108 to pass through when theconnector is turned (as illustrated by the arrows in FIG. 7) so that thebranches forming the “T” extend laterally. Mounting member 16 alsoincludes a post 25 that projects into aperture 21. Post 25 is sized tomate with an aperture 27 formed in projection 20 of abrading element 18as shown in FIG. 10. Projection 20 is also formed with a slot 29designed to receive connector 108 as described below.

With reference to FIG. 9, tubular member 100 fits within shaft 12 withconnector 108 extending from distal end 13 of the handle. Projection 20of abrading element 18 is inserted into aperture 21 of mounting member16 such that post 25 fits into aperture 27 of projection 20. Connector108 is initially rotated such that its “T” branch fits through slot 23of mounting member 16 and then is rotated 90° as shown by the arrows inFIG. 7. With the “T” branches of connector 108 extending parallel topost 25, projection 20 of abrading element 18 fits into aperture 21 ofmounting member 16 such that connector 108 fits into slot 29, and post25 fits into aperture 27.

FIG. 10 shows the same structure as FIG. 9 but with mounting member 16removed for purposes of better illustrating the mating of connector 108with slot 29. As shown in FIG. 10, pivot rod 114 fits into a matingaperture 115 formed at the distal end of shaft 12, and projection 20includes a second slot 120 formed laterally from slot 29. Slot 120 isconfigured to allow connector 108 to toggle back and forth as tubularmember 100 is reciprocatingly pivoted about pivot rod 114 by thedevice's drive mechanism. This “toggling” action of member 100 aboutpivot rod 114 moves T-shaped connector 108 and abrading element 18 inthe direction indicated by the double headed arrow in FIG. 10.

Of course, many variations exist for mechanisms to couple the drivemechanism 14 to abrading element 18. The coupling mechanism describedabove is provided by way of example and not limitation.

In the embodiment described, mounting element 16 may interchangeablyreceive various ones of abrading element 18. Thus, abrading element 18may be quickly and easily attached to and detached from mounting member16 during surgery. While in the preferred embodiment the abradingsurface of the abrading element is selected to have a width that issubstantially the same as the width of the surface to be formed in thevertebral end plate (to eliminate any need to move the abrading elementside to side in the disc space as noted earlier), a surgeon might alsoelect to use an abrading element that is smaller in width than theultimate desired width of the surface to be formed. Thereafter, thesurgeon may use successively larger abrading elements 18 until shearrives at the desired dimensions of the space formed between theadjacent bone structures. This approach also eliminates any need tosignificantly move the abrading element in a side to side path withinthe disc space.

Referring back to FIGS. 1 and 1A, device 10 includes at least one stopmember 28 adjustably disposed on mounting element 16 to limit the travelof the abrading element into the adjacent bone structures. Stop member28 includes an abutment 30 that will eventually contact the vertebrae tolimit travel of the abrading element 18 as the abrading element formsthe space between the adjacent vertebrae. Stop member 28 is not limitedto a single abutment. Two or even more abutments may be formed aroundthe circumference of stop member 28 and the leading edges of suchmultiple abutments may be configured to terminate at different positionsrelative to shaft 12. Other mechanisms for limiting the depth ofinsertion of the device into the disc space are possible, and thisexample is provided by way of illustration.

In the embodiment of stop member 28 shown in FIGS. 1, 2, and 3, a slot29 is formed in stop member 28 and an extension 31 projects from shaft12 through slot 29. Slot 29 is dimensioned to correspond to the desiredmaximum amount of adjustment of the stop member relative to the handle.As shown in FIG. 2, and in FIGS. 5 and 6, stop member 28 is held at adesired position on shaft 12 by spring-biased lever 32. Lever 32includes an actuator end 33 with grooves, notches, knurls, or othersurface preparation that is pushed toward shaft 12 against the bias ofspring member 34 to lift engaging end 35 of lever 32 away from shaft 12.Engaging end 35 is configured to mate with notches 36 formed in shaft 12as shown in FIG. 5. Notches 36 in shaft 12 are not visible in FIG. 2since they are covered by stop member 28. Step member 28 is also formedwith an opening sized to allow engaging end 35 of lever 32 to fit innotches 36. Numerous other structures for holding stop member 28 at adesired position on shaft 12 are possible, and spring biased lever 32 isprovided in this embodiment of the present invention by way of exampleand not limitation. For instance, shaft 12 may include threads on aportion of its outer surface to receive a threaded adjusting collar thatwill lock stop member 28 in a desired position.

With reference to FIGS. 21 and 22, examples of the types of motionthrough which abrading element 18 may be moved are illustrated. In FIG.21, the motion is vibratory in a plane generally parallel to theabrading surface of the abrading element. In FIG. 22, the motion islinear and reciprocating as indicated by the double headed arrow of thatfigure. Alternatively, the motion may comprise slight rotation about apivot point near distal end 15 of shaft 12 such that the oscillation isarcuate about an axis extending into and out of the sheet of paper onwhich FIGS. 21 and 22 are illustrated. Other motions such as full andcomplete rotation as described below with reference to the secondpreferred embodiment are also useful.

Any of these types of motion will be adequate to cause the abradingsurface or surfaces of abrading element 18 to abrade adjacent bonestructures to thereby form the appropriately sized and dimensioned spacebetween those bone structures for receiving an insert. In this regard,at least one or more of the surfaces of abrading element 18 is roughenedsuch that it can abrade the adjacent bone structures.

FIGS. 11, 12, 13, 14, and 15 illustrate various views of vertebralbodies that have been worked on by a device incorporating the presentinvention. The cross-hatching in these figures represents the softer,blood rich cancellous bone of the vertebrae beneath the harder, outercortical bone shell. FIG. 11 shows a top view of a first vertebral body70 With a surface 72 formed by a circular abrading element 18 as shownin FIG. 1. The width of surface 72 formed on first vertebral body 72closely matches the width of an abradirg element 18 that was advancedinto the disc space along a single front to back axis. A secondvertebral body 77 has a greater depth than vertebral body 70. The secondvertebral body 77 shown in FIG. 12 has a surface 75 formed by extendingabrading element 18 deeper into the distal interspace alongfront-to-back axis 74. FIG. 13 illustrates a cutaway side view of thevertebral body shown in top view in FIG. 12. FIG. 14 shows a cutawayside view of adjacent vertebral bodies 70 and 76 that have had surfaces72 and 78 formed in their respective adjacent end plates. Note that, asshown in exaggerated view in FIG. 15, the vertebral end plate surface isprepared to a uniform shape, which while preserving the deeper portionsof the end plate, also forms a socket depressed from the hard corticaluprisings of bone such as the uncovertebral joints 80. The socket formedhas a non-cylindrical shape transverse to the axis of insertion along amajority of the depth of the socket. Recognize that the depth of thisremaining end plate is exaggerated in FIG. 15 to illustrate this resultof using the present invention. This remaining portion of the morecortical rim 80 assists in retaining the insert in the desired positionbetween the adjacent vertebrae by acting as an abutment preventinglateral or posteriad movement of the insert. The prepared faces of theseabutment portions of the vertebral end plate also increase the surfacearea of contact between the insert and the vertebral body.

FIG. 15A illustrates, in top view, the ideal portion of a disc that isremoved to accommodate implantation of the insert. In FIG. 15A, theannulus fibrosus is illustrated with rings 200 extending around theperiphery of the intervertebral disc space. Inside the annulus fibrosusis the nucleus pulposus 202 illustrated in cross-hatching. The generalarea and volume of the nucleus pulposus to be removed with the device ofthe present invention is illustrated with additional cross-hatchings204. The preferred dimensions of the space created by the device isgenerally not as wide as the entire nucleus pulposus.

Referring now to FIGS. 16 and 17, a second embodiment of the presentinvention is shown wherein abrading element 18 includes two abradingsurfaces: an upper abrading surface 90 and a lower abrading surface 92.FIG. 16 is a top view of such a device and FIG. 17 is a side view. Inthis embodiment, abrading element 18 includes two disc shaped members,81 and 83, that are mounted on the distal and of the device by arecessed screw 147 and screw shaft 148 as described below. Abradingsurface 90 is formed on one side of disc-shaped member 81, and abradingsurface 92 is formed on one side of disc-shaped member 83. Thus, theabrading element 18 illustrated in FIGS. 16 and 17 provides an exampleof an instance where the abrading element comprises multiple pieces thatfit together to form the abrading element. As previously described, thepresent invention contemplates unitary, one piece constructions for theabrading element as well as multi-piece constructions. In the embodimentof the present invention shown in FIGS. 16 and 17, the upper and lowerdisc-shaped members 81 and 83 and their associated abrading surfaces maybe rotated in opposite directions so as to counteract and balance anytorque applied to the shaft and handle of the device as the abradingelement digs into and abrades the vertebral end plates. Thiscounter-rotation of the members 81 and 83 also prevents the device frombeing pulled to one side as the vertebral end plates are being workedon. This counter-rotating motion of the two members 81 and 83 isillustrated by the arrows in FIG. 17 and may be achieved, as illustratedin FIG. 17B, by using a spinning drive rod 160 that extends throughshaft 12 and is configured with a gear 162 at its distal end thatengages with mating gear teeth 93 and 94 formed on respective ones ofdisc-shaped members 81 and 83 as shown in FIGS. 17A and 17B. Disc shapedmembers 81 and 83 may be attached to the end of shaft 12 by a recessedscrew 147 that is received in a mating, threaded screw shaft 148 asshown in FIG. 17B. Thus, in this second embodiment, the mounting membercomprises threaded screw shaft 148 and recessed screw 147 disposed atthe distal end of a tapered extension 149 that protrudes from shaft 12.

FIGS. 16A and 17A show a further enhancement to the device shown inFIGS. 16 and 17 wherein the shaft 12 also includes an irrigation tube150 and a suction tube 152 that may be formed within, or outside of,shaft 12. These irrigation and suction tubes may be connected toappropriate sources of irrigation fluid and a source of vacuum,respectively, to efficiently irrigate and clear the surgical site duringuse of the device.

Alternatively, and as shown in FIG. 20, upper and lower disc-shapedmembers 95 and 96 may be formed with inwardly sloping, ramped surfaces97 and 98 that engage a cone-shaped driver 99 disposed on the distal endof a rotating drive rod 160 to turn the upper and lower abradingsurfaces in opposite directions as the drive rod spins about its axis.Alternatively, the lower surfaces of the abrading element 18 and thecone-shaped driver can be radially splined to engage one another. Such adual surface abrading element can simultaneously work on both adjacentend plates of adjacent vertebrae. Abrading member 18 having such dualabrading surfaces can even be constructed such that the distance betweenthe abrading surface is adjustable to accommodate variations in theheight of the disc space. By way of example and not limitation, paired,wedge-shaped blocks may be disposed between the abrading surfaces and anadjusting screw can be provided to extend through threaded apertures ineach wedge-shaped block. As the adjusting screw is turned, thewedge-shaped blocks move relative to one another to change the distancebetween the abrading surfaces.

In a still further embodiment of the present invention as illustrated inFIG. 18, the abrading element 18 may have upper and lower abradingsurfaces 140 and 142 that are angled or tilted relative to each other.The degree of angle or tilt may be selected to match the naturallordotic curvature of the spine at the location of the vertebrae to beworked on. The distance between the upper and lower abrading surfaces140 and 142 in this embodiment may also be adjustable to accommodatediffering disc heights between the vertebrae. Such angled abradingsurfaces may also be driven in counter rotation by drive rod 160 asshown by the arrows in FIG. 18. As illustrated in FIG. 19, the slope ofthe surfaces 144 and 146 formed in the adjacent vertebrae by theabrading element shown in FIG. 18 matches the lordotic curvature of thespine at that location.

Numerous other configurations of abrading element 18 are possible withinthe scope of the present invention. For example and with reference toFIG. 23, abrading elements 218 may be convex to form concave receivingsurfaces 220 in the vertebral end plates. The geometry and configurationof the shapes of the abrading elements can be matched to the desiredshape and configuration of the space which the surgeon intends to createbetween adjacent bone structures and to the desired contour of thesurfaces created in the bone structures.

Additionally, the abrading surface of abrading element 18 may beconfigured as roughenings, knurls, ridges, small pyramid shapedprojections, or any other surface configuration that is capable ofabrading the bone structures.

Where only one surface of the abrading element is configured to abradean end plate of the vertebral body, an opposite surface (or the oppositesurface of mounting member 16 as illustrated by element 17 in FIG. 2)may be configured to be supported by the adjacent end plate withoutcausing any significant abrasion of that adjacent end plate. In such aninstance, the non-abrading surface of the abrading element, or surface17 of mounting member 16, may be configured to allow the surgeon toachieve a mechanical advantage that increases the bearing pressure ofthe abrading surface against the end plate being worked on, and also tolocate and center the device. In this manner, one adjacent end plateprovides mechanical support to the device while the device works on theadjacent end plate. After an appropriate surface is formed on one endplate, the device can be turned 180° to use the abrading surface on theother end plate.

Since any device incorporating the subject matter of the presentinvention is designed to be used within a surgical theater, it isdesirable that the device be susceptible of sterilization by any one ofmany known expedients. In this regard, handle 12 of device 10 may bewaterproof such that the device can be sterilized.

Although various embodiments of the present invention have beendisclosed for purposes of illustration, it will be understood by thoseof ordinary skill in the art that changes, modifications, andsubstitutions may be incorporated in these embodiments without departingfrom the spirit or scope of the present invention as defined by theclaims, which follow.

1. A method for performing surgery on a spinal segment including a discspace and two vertebral bodies adjacent the disc space of a human spine,said method comprising the steps of: forming a socket by removing bonefrom at least a portion of at least one of the adjacent vertebral bodiesfrom within the disc space and between the external perimeters of thetwo adjacent vertebral bodies, the socket formed in the bone having anentrance, an abutment wall formed in the bone opposite the entrance, anaxis of insertion through the entrance and the abutment wall, and adepth along the axis of insertion, the abutment wall having a height anda width, the socket having a surface formed in the bone from theabutment wall to the entrance and extending from the side to the side,the surface having a plurality of points in a horizontal plane thatpasses through the surface, the horizontal plane being parallel to theaxis of insertion and being perpendicular to a vertical plane thevertical plane passing through and being parallel with the axis ofinsertion and passing through the adjacent vertebral bodies the abutmentwall being in the shape of approximately one half of a circle from sideto side in the horizontal plane; and inserting a spinal insert into thesocket, the spinal insert having a leading end and a trailing endopposite the leading end, the leading end of the insert having anexterior configured to substantially correspond to the shape of theabutment wall of the socket.
 2. The method of claim 1, wherein the stepof forming includes removing bone from at least a portion of each of theadjacent vertebral bodies.
 3. The method of claim 2, wherein the step offorming includes forming the socket to have upper and lower surfacesthat are angled relative to one another.
 4. The method of claim 2,wherein the step of forming includes forming the socket to have upperand lower surfaces that are generally parallel relative to one another.5. The method of claim 1, wherein the step of forming includes formingthe socket to have at least one of an upper surface and a lower surfacethat is at least in part concave.
 6. The method of claim 1, wherein thestep of forming includes forming the socket to have at least one of anupper surface and a lower surface that is at least in part planar. 7.The method of claim 1, wherein the step of forming includes forming thesocket to have a distance between the entrance and the abutment wallthat is greater than one-half the width of the abutment wall.
 8. Themethod of claim 1, wherein the step of forming includes forming thesocket to have a distance between the entrance and the abutment wallthat is greater than the width of the abutment wall.
 9. The method ofclaim 1, wherein the spinal insert is an artificial disc.
 10. The methodof claim 1, wherein the spinal insert is a motion preserving device. 11.The method of claim 1, wherein the spinal insert is a bone graft. 12.The method of claim 1, wherein the spinal insert is a fusion implant.13. The method of claim 1, further comprising the step of combining thespinal insert with a fusion promoting material.
 14. The method of claim13, wherein the spinal insert includes a hollow portion and the step ofcombining includes packing the spinal insert with the fusion promotingmaterial.
 15. The method of claim 13, wherein the fusion promotingmaterial is bone.
 16. The method of claim 1, further comprising the stepof suctioning debris from the socket.
 17. The method of claim 1, furthercomprising the step of imigating the socket.
 18. The method of claim 1,wherein the step of forming includes removing bone with a device that ismechanically driven.
 19. The method of claim 18, wherein the deviceincludes an abrading element.
 20. The method of claim 1, wherein thestep of forming includes forming the socket to have opposed side wallsbetween the entrance and abutment wall, at least one of the side wallsbeing at least in part straight.
 21. The method of claim 20, wherein thestep of brining includes forming the socket to have at least one of anupper surface and a lower surface that is at least in part concave. 22.The method of claim 20, wherein the step of forming includes forming thesocket to have at least one of an upper surface and a lower surface thatis at least in part planar.
 23. The method of claim 20, wherein the stepof forming includes removing bone from at least a portion of each of theadjacent vertebral bodies.
 24. The method of claim 23, wherein the stepof brining includes forming the socket to have upper and lower surfacesthat are angled relative to one another.
 25. The method of claim 23,wherein the step of brining includes forming the socket to have upperand lower surfaces that are generally parallel relative to one another.26. The method of claim 1, wherein the step of forming includes fanningthe abutment wall with a first arc of radius from side to side and asecond arc of radius from side to side that is spaced from the first arcof radius along the height of the abutment wall, the first and secondarcs of radii being the same.
 27. The method of claim 1, wherein thestep of forming includes forming the socket to have a non-cylindricalshape transverse to the axis of insertion along a majority of the depthof the socket.
 28. The method of claim 1, wherein the step of formingincludes forming the surface of the socket to be at least in part curvedin a plane parallel to the axis of insertion.
 29. The method of claim 1,wherein the step of forming includes forming the socket to have upperand lower surfaces that are at least in part curved in a plane parallelto the axis of insertion.
 30. The method of claim 1, wherein the step offorming includes removing bone from at least a portion of each of theadjacent vertebral bodies.
 31. The method of claim 30, wherein the stepof forming includes forming the socket to have upper and lower surfacesthat are angled relative to one another.
 32. The method of claim 30,wherein the step of forming includes forming the socket to have upperand lower surfaces that are generally parallel relative to one another.33. The method of claim 1, wherein the step of forming includes formingthe socket to have a distance between the entrance and the abutment wallthat is greater than the width of the abutment wall.
 34. The method ofclaim 1, wherein the spinal insert is a bone graft.
 35. The method ofclaim 1, wherein the spinal insert is a fusion implant.
 36. The methodof claim 1, further comprising the step of combining the spinal insertwith a fusion promoting material.
 37. The method of claim 36, whereinthe fusion promoting material is bone.
 38. A method for performingsurgery on a spinal segment including a disc space and two vertebralbodies adjacent the disc space of a human spine, said method comprisingthe steps of: forming a socket by removing bone from at least a portionof at least one of the adjacent vertebral bodies from within the discspace and between the external perimeters of the two adjacent vertebralbodies, the socket formed in the bone having an entrance, an abutmentwall formed in the bone opposite the entrance, an axis of insertionthrough the entrance and the abutment wall, and a depth along the axisof insertion, the abutment wall having a height and a width, theabutment wall being in the shape of approximately one half of a circlefrom side to side in a horizontal plane that is parallel with the axisof insertion and passes through the abutment wall of only one of theadjacent vertebral bodies, the socket having a surface formed in thebone from the abutment wall to the entrance and extending from the sideto the side, the surface being at least in part planar; and inserting aspinal insert into the socket, the spinal insert having a leading endand a trailing end opposite the leading end, the leading end of theinsert having an exterior configured to substantially correspond to theshape of the abutment wall of the socket.
 39. A method for performingsurgery on a spinal segment including a disc space and two vertebralbodies adjacent the disc space of a human spine, said method comprisingthe steps of: forming a socket by removing bone from at least a portionof at least one of the adjacent vertebral bodies from within the discspace and between the external perimeters of the two adjacent vertebralbodies, the socket formed in the bone having an entrance, an abutmentwall formed in the bone opposite the entrance, an axis of insertionthrough the entrance and the abutment wall, and a depth along the axisof insertion, the abutment wall having a height and a width, theabutment wall being in the shape of approximately one half of a circlefrom side to side in a horizontal plane that is parallel with the axisof insertion and passes through the abutment wall of only one of theadjacent vertebral bodies, the socket having a surface formed in thebone from the abutment wall to the entrance and extending from the sideto the side, the surface being at least in part curved in a planeparallel with the axis of insertion; and inserting a spinal insert intothe socket, the spinal insert having a leading end and a trailing endopposite the leading end, the leading end of the insert having anexterior configured to substantially correspond to the shape of theabutment wall of the socket.
 40. The method of claim 39, wherein thestep of forming includes removing bone from at least a portion of eachof the adjacent vertebral bodies.
 41. The method of claim 40, whereinthe step of forming includes forming the socket to have upper and lowersurfaces that are angled relative to one another.
 42. The method ofclaim 39, wherein the step of forming includes forming the socket tohave at least one of an upper surface and a lower surface that is atleast in part concave.
 43. The method of claim 39, wherein the step offorming includes forming the socket to have a distance between theentrance and the abutment wall that is greater than the width of theabutment wall.
 44. The method of claim 39, wherein the spinal insert isa bone graft.
 45. The method of claim 39, wherein the spinal insert is afusion implant.
 46. The method of claim 39, further comprising the stepof combining the spinal insert with a fusion promoting material.
 47. Themethod of claim 46, wherein the fusion promoting material is bone.